The present invention relates to a rod clamp apparatus of the type having an annular rod clamp ring and an annular cam movable axially in one direction relative to the clamp ring to a clamp position, and in an opposite direction to a clamp release position. Some rod clamps have used antifriction bearings arranged for rolling engagement between the annular cam and rod clamp ring to reduce frictional resistance to axial movement of the cam between the rod clamp and rod release positions. The antifriction bearings roll lengthwise of the cam during axial movement of the cam and grooves or recesses have heretofore been provided in the clamp ring for guiding the antifriction bearings along circumferentially spaced paths. However, if the antifriction bearings in one or more of the grooves become displaced in a longitudinal direction relative to the antifriction bearings in other circumferentially spaced grooves, the radial forces applied by the annular cam through the antifriction bearings to the clamp ring will not be uniformly distributed around the piston rod and may cause erratic clamping or release of the rod.